Electric gas discharge tube



March 30, 1948. P. SCHOUWSTRA (I ELECTRIC GAS DISCHARGE TUBE Filed March50, 1946 INVENTOR: PIETER SCHOUWSTRA BY I .515 ATTORNEY Patented Mar.30, 1948 ELECTRIC GAS DISCHARGE TUBE Pieter Schouwstra, Eindhoven,Netherlands, assignor to General Electric Company, Schenectady, N. Y.

Application March 30, 1946, Serial No. 658,408 In the Netherlands June16, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires June16, 1962 The invention relates-to electric gas discharge tubescomprising an incandescent electrode and a thermal switch which reactsto the temperature of this electrode. By electric gas discharge tubes"are meant hereinafter not only discharge tubes filled with one or moregases-but also tubes filled with vapour or with a mixture of gas andvapour.

The invention relates to an improvement in these discharge tubes.

According to the invention, the switch is constructed and arranged insuch manner that the incandescent electrode is invisible from thedischarge path. Owing to this arrangement there is achieved anarrangement wherein the particles disintegrating from the electrode areintercepted in the direction of the discharge path and wherein anassociated switch has two functions. There is therefore no need forproviding a separate screen for intercepting the disintegrated cathodeparticles. The switch may be constructed in such manner that theincandescent electrode is also invisible from the directionperpendicular to the discharge path and is accessible from the directionaway from the discharge path. It is thus achieved that the dischargealso appears hehind the electrode so that the presence of dark ends ofthe tube may be avoided.

In one advantageous form of construction of the gas discharge tubeaccording to the invention the element responsive to heatsemi-cylindrically surrounds the incandescent electrode which extendsperpendicularly to the discharge path and this element may be providedwith sidefiaps or positionable appendages integral with the shieldstructure which cover the ends of this semi-cylinder.

The switch responsive to the temperature of the electrode may beutilized for different purposes. It may serve, for example, to put thedischarge path under tension, to alter the heating of the electrode orof a supply which gives 01! metal vapour or of a substance evolving gas,to act upon an ignition mechanism, to switch into c rcuit a coolingdevice of the tube, to connect the two ends of the electrode to oneanother after the discharge has occurred, etc. In some of these casesthere may occur the risk of the production of a discharge between theincandescent electrode and one of the contact pieces of the switch. Thismay be avoided by housing that contact piece of the switch which issecured to the ther mally responsive element arranged in the dischargechamber and serving to screen the incandescent electrode, and also thecounter contact 6 Claims. (C1.17c 122) 2 piece in a chamber ofinsulating material which communicates with the discharge chamber via anarrow aperture which is partly closed by the said Contact piece.

According to one particular embodiment of the invention, the contactchamber may have a cylindrical shape and the contact piece may bemovable in the axis of the chamber. It is thus possible to reduce theaperture by means of which the Contact chamber communicates with thedischarge chamber, to a minimum without retardmg or hindering themovement of the contact member. Accordingly, a very simple constructionof a contact chamber may be obtained by using a glass tube one end ofwhich is sealed to the pinchor disc-shaped end of the tube which carriesthe incandescent electrode, as disclosed and claimed in U. S. Patent2,313,683, filed by R. N. Thayer and assigned to the assignee oi'thisapplication. In some cases it is still simpler to utilize a cylindricalcavity or this pinchas the contact chamber.

If one of the contacts or the thermal switch has to be connected to thenon-adlacent electrode, this may advantageously be effected by means ofa conductor which is secured to or in the discharge tube itself. By thismeans radio interferences caused by the tube are reduced. In addition,this procedure facilitates the ignition and the re-ignition oi the tube.The circuit arrangement of the tube may also be simplified by thisprocedure because this conductor may connect the two electrodes of thetube via the switch without any need of utilizing for this purpose a,

particular conductor outside the tube. Under certain circumstances thepresence of the conductor on the outside 01' the wall may be moreadvantageous than on the inside of the discharge vessel. In the lattercase it is more difficult to insulate the conductor from the dischargeand, in addition, there arise other disadvantages, for example, thoseassociated with providing and maintaining a luminescent layer of powderon the inside of the wall of the discharge vessel. The conductor may beprovided on the outside of the wall by sealing it thereto by means of akind of glass of low melting-point or by securing it thereto with theaid 0! an insulating and ference. According to one advantageousembodiment of the invention. a condenser of, say. from 5000 to 50,000mo. which shunts the switch and, as the case may be, also theincandescent electrode, is incorporated in a stem tube or a cap of thedischarge tube, It is thus achieved that all the elements necessary forthe operation or the tube, with the exception of the steadyingseries-impedance, are united with the tubeso that it suffices to utilizetwo supply conductors, two connecting members of the tube and twoconnecting members in the holder orholders of the tube, which simplifiesthe component parts and facilitates the mounting of the tube. Byincorporating also the steadying series-impedance of the tube in theholder or holders, it is achieved that the mounting is as simple as thatof an incandescent lamp.

The invention will be explained more fully with reference to theaccompanying drawin which represents, by way of example, one embodimentthereof.

Figure 1 represents a low-pressure mercury-vapour discharge tube servingfor the radiation of light, which tube substantially consists of a glasstube I having, for example, an external diameter of 35 mms. and a lengthof 100 cms. This tube is hermetically closed at either end and comprisesincandescent or thermionic electrodes 2 and 3 of the usual type. Thetube contains a small or low melting-point. Figure 2 shows in section aportion 01 the wall or the tube with the conductor I4. Those portions ofthe wires and I3 which are remote from the discharge chamber areconquantity of mercury whichyields the required v mercury vapour with anoperating pressure of about 0.01 mm. of mercury and, in order tofacilitate the ignition, it may be filled, in addition, with a gasmixture consisting for example of neon and argon and having a pressureof a few mms. On the inside of the wall the tube may be coated with aluminescent layer or it may consist of luminescent glass.

The electrode 2 ismounted on supporting wires 4 and 5 which hermeticallypass through the pinch 6 of a stem tube I. A bi-metallic element 9 whichsemi-cylindrically surrounds substantially the full length of theelectrode 2, which extends perpendicularly to the axis of the dischargepath, in the direction of the electrode 3, is secured to the supportingwire 5 through the intermediary of a wire 8 which is bent at a rightangle. Thebi-metallic element 9, for example, may be a shield concavetoward the press or pinch 6 and, may be provided with two side-flaps Inwhich shut the side-apertures of the semi-cylinder; for the sake ofclearness the'right-hand side-flap is shown in a plane parallel to thesupporting wire. To the front-side of the bi-metallic element 9 issecured the upper end of a wire II which has been bent twic at a rightangle and the lower end of which acts as a contact piece and is movablelike a piston in 8. cylindrical cavity I2 of the pinch 6. Into the lowerpart of this cavity I2 protrudes a supply wire I3 whose upper endconstitutes the counter contact piece of the switch. The supply wire I3may, for example, be hermetically provided. by means ofa glass bead, inan originally throughgoing bore I2. Instead of the cavity I2 of thepinch 6 use might also be made of a tube of insulating material, forexample glass, which is secured to the upper-side or under-side of thepinch or to another hermetically obturating member of the tube end. Thatend of the supply wire I3 which is remote from the discharge chamber isconnected to the electrode 3 by means of a conductor I4 which is securedto the outside of the tube I with the aid of an insulating andpreferably transparent strip I5 which may consist, for example, of akind of glass nected to another by means of a condenser I6 of the orderof magnitude of 0.01 at. This condenser shunts the contact pieces II andI3 via the wire element 9 and can easily be housed in-the hollow spacebetween the stem tube 1 and a cap I'I. It

would also be possible to connect this condenser,

which acts as a capacity for eliminating radio interferences, betweenthe wires 4 and I3, in which case the contacts are shunted by thecapacity I6 plus the resistance of the electrode 2.

To the supporting wire 4 of the electrode 2 may be secured a wire-shapedauxiliary contact I8 and this in such manner, that it makes contact withthe central piece of the wire II which has been bent twice at a rightangle, after the'bi-metallic element 9 has attained the position ofordinary source of current is connected, through the intermediary of achoke coil 24, to that end of the electrode 3 which is remote from theconductor I4. The choke coils 20 and 24 or a single choke coilsubstituted for them may be housed in the holders I9 and/or 25, in whichcase the mounting -of the tube I is as simple-as that of a tubularincandescent lamp. 4

The device operates as follows: I n-the cold condition of the bimetallicelement the ends of the wires II and I3 are in contact with one anotherso that, after the main switch 2I has been closed, the incandescentelectrodes 2 and'3 are traversed by a series-current which is substantially determined by the impedance of the electrodes and the chokecoils. This current rapidly raises the electrodes; to the emissiontemperature whereby the bimetallic element 9 undergoes'a deformationsuch that the contact piece. II- is drawn away from the counter contactpiece I3 with the result that the mutual connection between the twoelectrodes is broken so that the discharge path is no longershort-circuited and the tube can be ignited, which is facilitated by avoltage impulse which is furnished by the choke coils upon theinterruption of the said series cir cuit. During the normal operationthe electrode 2 is heated exclusively by the discharge. The bimetallicswitch is kept open in this case by the heat given out by'the electrode2 and by the heat pair of cooperating'electrodes at least one of whichis a thermionic electrode supported by a stem press, a bimetallic shieldconcave toward said press and extending about substantially the fulllength. or said thermionic electrode. the other one of said cooperatingelectrodes being positioned so that it faces the convex side of saidshield, and contact means actuated by said shield.

2. An electric discharge device comprising a pair of cooperatingelectrodes at least one of which is a thermionic electrode supported bya stem press, a closed-end semi-cylindrical bimetallic shield concavetoward said press and extending about substantially the full length ofsaid thermionic electrode, the other one of said cooperating electrodesbeing positioned so that it faces the convex side of said shield, andcontact means actuated by said shield.

3. electric discharge device comprising a pair of cooperating electrodesat least one of which is a thermionic electrode supported by a stempress, a closed-end semi-cylindrical bimetallic shield concave towardsaid press and extending about substantially the full length of saidthermionic electrode with the axis of the electrode perpendicular to thearc discharge path, the other one of said cooperating electrodes beingpositioned so that it faces the convex side oi. said shield, and contactmeans actuated by said shield.

4. An-electric discharge device comprising a pair of cooperatingelectrodes at least one of which is a thermionic electrode supported bya stem press, a bimetallic shield concave toward said press andextending about substantially the full length of said thermionicelectrode, the other one of said cooperating electrodes being positionedso that it faces the convex side of said shield, a stationary contactmounted in a cavity in said press,

- and a movable contact means actuated by said shield for engagementwith said stationary contact,

5. A gaseous electric discharge device comprising a sealed envelopecontaining cooperating electrodes at least one ofwhich is a thermionicelectrode, a switch comprising a bimetallic member mounted within saidenvelope and in heat-receiving relation to said thermionic electrode,saidbione end or said thermionic electrode, contact means carried by andactuated to open-circuit position by said bimetallic member upon heatingthereof, and means electrically connecting said bimetallic member withthe other end ofsaid thermionic electrode upon expansion of saidhimetallic member to short-circuit said electrode during operation ofthe device.

6. An electrode structure for an electric discharge device comprising incombination a vitreous stem, a pair of lead-in wires fused to said stem,a support wire fused to said stem, a thermionic electrode connected toand between one of said lead-in wires and said support wire, abimetallic member concave toward said stem and enclosing said thermionicelectrode, said bimetallic meme ber being supported at one end from saidsupport wire and electrically connected to the adjacent end of saidthermionic electrode, movable contact means carried by the other end orsaid bimetallic member and normally engaging one end of said otherlead-in wire, and a second contact member on said one lead-in wirelocated in the path of movement of said movable contact means toelectrically connect said bimetallic member with the other end oi. saidthermionic electrode upon expansion of said bimetallic member toshort-circuit said electrode during operation of the device.

PIETER SCHOUWS'I'RA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

